Let me introduce you to a great math book entitled "Easy As Pi" by Liz Strachan, an experienced math teacher from Scotland. The book was first published in 2016 by Robinson. A funny cover was designed by Bekki Guyatt, and illustrations were made by Steven Appleby.
Good to know that the book is available both as hardcover and an e-book in the Kindle format edition which makes it pretty convenient either way you like it. 
In order to encourage you to go read the book, I am here briefly mentioning a few problems discussed in it and some others just inspired by Liz's work.